1. Field of the Invention
This invention relates to a liquid crystal composition for use in a ferrodielectric liquid crystal display element, etc.
2. Description of the Prior Art
Recently, various liquid crystal compositions which exhibit ferrodielectric property have been proposed. However, there is scarcely a liquid crystal composition which has preferable orientation and responsiveness, and a lower limiting temperature of the chiral smectic C (Sc*) phase presented at room temperature or lower.
For example, according to Goodby et al proposal, when compounds A, B, C represented by the following formulae (A), (B) and (C) are mixed, a liquid crystal composition which has preferable orientation and responsiveness can be prepared, where symbols S and R in the following formulae respectively indicate that the absolute dispositions of optical active groups of side chains are S type and R type. ##STR2##
However, when the relationship between the transfer temperature and the mixture ratio of the liquid crystal composition made of these compositions A, B and C is examined, the temperature range exhibiting Sc* phase is approx. 13.degree. to 55.degree. C. in the best state as shown in FIG. 5. (The liquid crystal composition measured in this proposal was prepared by adding the compound C to the mixture Z mixed with the compounds A and B at the ratio of A:B =4:6 (molar ratio).)
The temperature range of the Sc* phase of a liquid crystal composition obtained by mixing liquid crystal compounds D and E represented by the following formulae (D) and (E) is approx. 20.degree. to 65.degree. C. in the best state as shown in FIG. 6. ##STR3##
On the other hand, there is also a proposal that the temperature range of Sc* phase can be increased by mixing a compound having a different skeleton. The temperature range of Sc* phase of a composition obtained by mixing the compounds A to E according to this proposal is approx. 0 to 63.degree. C. in the best state as shown in FIG. 7. (The liquid crystal composition measured in this proposal was prepared by adding a mixture X mixed with the compounds D and E at the ratio of D:E=8:2 (molar ratio) to the mixture Y mixed with the compounds A, B and C at the ratio of A:B:C =37:55.5:7.5 (molar ratio.)
As described above, the conventional ferrodielectric liquid crystal composition is unstable in practical use since the lower limiting temperature of the Sc* phase is not sufficiently low.